The shower sump on my 58MY is a pit in the master SR floor on center between the foot of the bed and the closet. It's actually below the normal surface of the fiberglass surface in the hull. Imagine looking in the aft section of your bilge where you'd find your aft bilge pump, strut bolts sticking up, etc. Well, built into that on the centerline is a sump pit that is lower than the surface where the two showers, the master and one of the guest guest showers, drain. It's not all that deep and is the easiest, most accessible bilge pump to service in the whole boat. Down there, I have a Rule 2000 pump with an automatic float switch so I do not have to run the sump constantly via the manual switch when showering. Yes, that pump is somewhat overkill for that area, but it's another bilge pump if and when I really need one. In fact, that pump will cycle BEFORE my aft bilge pump does. When I see my aft bilge pump light on, I do tend to panic because my shower never lets water reach that one, except when something goes very wrong. So, I do like having the big pump in the very lowest point in the boat. To cure the backwash of water from the hose that Pascal describes which could result in frequent cycling, I installed a check valve on this particular pump. I have the same set up for my two forward showers. My shower head is a 2.5 gpm. Most moderns ones today are in that range, unless you get one of those designer massive waterfall heads.