If your rabbit has a messy bottom due to either runny stool or urine leakage, the most important thing to do is to determine the source of the problem, starting with a full exam by your rabbit-experienced veterinarian, including a full dental examination (including molars) as well as blood chemistry and blood cell counts. This can reveal undetected health problems that are manifesting as gastrointestinal or urinary tract signs. Treating these will be the ultimate way to solve the messy bottom problem.
Consideration of your bunny's physical and emotional well-being during a bath are of utmost importance. Whenever you handle your bunny, it's important to be firm, gentle and ready to release the bunny safely at ground level if she starts to struggle. One unexpected kick can subluxate or even fracture the spine if the bunny is not being held correctly. Believe it or not, a bunny's stress at being restrained against her will can actually kill. Never force your bunny to submit to any procedure if she is unduly upset by it.
That said, a messy bottom is both uncomfortable and unsanitary, inviting worse problems such as skin scalding and even fly strike. Relieving this problem while your vet does the detective work to find out the root of the problem will keep your bunny comfortable. One way is with a careful, gentle "butt bath" to keep caustic bodily fluids away from the skin. There are two methods one can safely use to clean a messy bunny bum: Dry or Wet.
1. Purchase Baby Cornstarch Powder (scented or unscented) from your local supermarket or drug store (baby supplies section).
2. Place bunny is a comfortable, belly-up position so that the soiled parts are easily visible and accessible. Be sure bunny's back is cushioned and that the back and neck are well supported to prevent any injury from a swift kick. Talk soothingly to let bunny know all is safe. If bunny struggles, never force him/her to stay in this position! Avoid stress or injury, above all. Let bunny get up, and then calmly and gently try again.
3. Apply cornstarch powder liberally to the soiled areas, and gently work the powder around dried poops, into the fur, and down to the skin. (If you have someone available to help, have that person use a hand-held vaccuum to suck up the floating powder, so that neither you nor bunny inhales much of it. Even cornstarch can be a respiratory irritant, and the less inhaled, the better.
4. Work the powder around any stubborn clumps of debris gently. As the powder coats the mess, it should release from the fur and slide away easily.
5. If necessary, use a fine-toothed flea comb to gently tease dried poop or other debris out of the fur. Don't pull too hard, as a bunny's delicate skin can tear surprisingly easily.
6. Pat the powdered areas well to remove loose powder. Use that hand-held vaccuum to remove floating powder from the air around the bunny.
With this technique, Bunny should be clean and dry in just a few minutes. Rabbits generally don't seem to mind a dry bath, and most will lie quietly as the soothing powder takes away the sting of urine burn.
1. Use a hypoallergenic, non-medicated shampoo.
2. Fill a clean bathroom sink to about 2.5" depth with slightly warm water (about 90oF)
3. Add about a tablespoon of shampoo to the bath water, and mix well.
4. Keep one arm wrapped around the bunny, under the bunny's elbows, and bunny's head and shoulders against your chest, with your other hand supporting the bunny's rear end. As always, be firm and gentle so that bunny can't jump and be injured. Bend over towards the sink and lower bunny's back end into the warm bath. When bunny's feet touch the bottom of the sink, you can release the hand holding her bum and use it for washing. (But always be ready for that unexpected jump!)
5. Gently lave the solution onto the soiled areas to remove the mess. There is no need to go beyond the soiled areas: it is not advisable to wet the bunny any higher up than the tail and lower tummy. If the bunny is very messy, you may have to change the water and repeat this procedure a few times until the water is clean when bunny is lifted out of the bath.
6. To rinse, fill the sink with slightly warm water again, but no shampoo. Lower bunny's bum into the clear bath and rinse well, laving with your free hand. You may have to drain the water and repeat this several times until the rinse water is free of any bubbles or shampoo residue. Be sure to rinse all washed areas well so that no shampoo remains.
7. Lift bunny out of the bath and very gently wring water out of the wet fur with your hands, supporting the rear end with your elbow. You can squeeze legs and feet very gently, as well, but be considerate of your bunny's sensitive areas. If s/he objects, don't insist. A towel will have to do the job.
8. Place bunny on a soft, cushioned surface with traction and towel-dry all wet areas carefully. Be sure not to rub too hard against irritated skin. Soft cotton or absorbent microfiber towels work well for this purpose.
9. Once bunny's fur is towel-dry, finish with a blow dryer on warm, not hot. If possible, use a dryer with a stand attachment so you'll have both hands free for grooming.
10. Keep your hands close to the area where dryer air is blowing, so you can monitor temperature. Adjust as necessary, making sure never to let hot air contact the skin. A fine-toothed flea comb can help separate the fur for quicker drying, but be careful not to pull too hard and tear delicate skin. Be sure to dry between skin folds, since moisture there can cause further irritation.
11. Once bunny is fluffy dry, you may wish to trim the fur away from areas where skin is irritated. Do this with blunt-tipped hair trimming scissors, and never trim where you can't see. If you can't see the skin, or are doubtful where skin ends and fur begins, then do not clip! Rabbit skin is extremely thin and elastic, and even a small wound can expand to alarming proportions! Don't take chances. If you're not confident you can do this without injuring your bunny, then skip this step.
12. Apply a very thin layer of soothing balm, such as calendula cream (from a natural foods store) or triple antibiotic ointment (with no topical anesthetic added!) to areas where skin is red or irritated. A little goes a long way.
You can repeat the wet bath procedure as necessary (some bunnies need bathing twice a day, though this is unusual), but do not continue if the rabbit seems unduly stressed by the experience. Bunny's safety is always paramount.
Remember: the "butt bath" is merely treating the symptom of what might be a more complicated disorder. It's important to discover why your bunny has urinary incontinence or runny stool (usually cecal), and get to the root of the cause for a complete cure.