We think there's a leak - need advice!

[louwho99]

I really hate to talk about this topic, but we have a problem & don't know how to fix it, so here goes.
We have a 2008 MS 38RLSB3. There is a terrible odor of urine coming from the pantry area. The bathroom is right behind the pantry so we assume there are toilet plumbing pipes behind the pantry wall, and we assume that a pipe is leaking. There is no odor in the bathroom.
My husband looked in the underbelly back in where the furnace is, but can't seem to see the pipe coming from the toilet.
If the leak is behind the pantry wall, is there a way to take the back of the pantry off?? We don't see any kind of access panel on the pantry wall.
Any advice on how to begin to find this leak & fix this problem is most appreciated. My husband is very handy & I'd bet he could fix it, but we need some guidance to get started. Calling a mobile RV tech is expensive & we don't really want to do that, if we can avoid it.
Thank you so much for any guidance you can provide!

Cindy