It's usually where the shower is in the horse compartment. Had a Cherokee trailer that had the RV type shower in a keyed box in the first stall compartment with a shower pan and drain from the first stall compartment on the floor. Water drained from the pan, into a plumbing hole in the floor and under the trailer.

Some folks just let the water drain out the back of the trailer too.

ponytammy.....thanks for the heads up....i think from what i've read you and your hubby are experts....i haven't trail rode since i was much younger but have been wanting to get back into it....been showing several years and miss the piece and quiet.... plan on starting out small but i don't figure it will take long before i get a need for more than a couple of hour ride....