The Drain Game
Route your water the right way with a shower sump pump.
by Chris Caswell
May 1, 2004
A shower on board is a luxury, but it can be difficult to drain the water. Some builders let
the water empty into the bilge, which will lead to a smelly and soapy bilge. Others require you to
flip on a pump switch to empty the shower, but if you turn it off too soon, you'll leave a cold
puddle for the next person. A better solution is to install an automatic shower sump pump. This has
an enclosed sump box that prevents water from escaping into the bilge and a float switch that turns
the pump on and off automatically. The sump system can also handle drain water from the sink or
galley.
Step 1:
A 12-volt Attwood Shower Sump System (#4137) is used in this example, but there are similar
units you can use from West Marine and Rule (price ranges from about $90 to $115). The sump box
must be located lower than the shower drain, and it should be level or no more than 1/2 inch higher
at the end without fittings. On most boats, you'll need to use a 1/2-inch mounting pad for the sump
box, shown here in the example of marine plywood. To install the mounting pad, sand the gel coat or
paint off the mounting surface, and use fiberglass mat or roving and resin to completely
encapsulate the wood block (not shown).
Step 2:
Position the sump box in the desired position with the clear top in place. When positioning
the sump box, make sure that the inlets and hoses will be accessible should you need to get to them
for maintenance, and that there is sufficient room to allow the hoses to curve without kinking,
which could cause some problems for drainage. There should also be enough room to remove the clear
top to clean the pop-out filter when needed. Mark and drill the pilot holes for the four
stainless-steel round-head screws in the hold-down clamps. Be particularly careful not to drill
into the hull.
Step 3:
Connect the 3/4-inch outlet hose by sliding the hose onto the barbed fitting and secure it
with a stainless-steel hose clamp. Lead the outlet hose to a through-hull fitting. Note that up to
three inlet hoses can feed into the sump, and these are also tapered to fit several hose sizes. Saw
off the plastic cap on the inlet to match the size of hose you are using for your project: 3/4
inch, 1 inch, 1 1/8 inch or 1 1/2 inch. Cut only as many inlets as you need. If you cut one inlet
and decide not to use it, make sure that you seal it with silicone sealant. Slide on the inlet
hoses, and secure them with stainless-steel hose clamps.
Step 4:
The 12-volt circuit must have a 4-amp fuse and an on-off switch for use in an emergency. The
switch can be mounted near the shower, but here the pump is wired directly to the Blue Seas circuit
breaker panel. A 16-gauge Ancor marine wire is used for the connections with crimp-on connectors.
The black wire goes to the negative bus on the panel, while the brown wire (here changed to red for
positive) goes to the positive bus. Pre-wire the system before clamping the sump in place. With the
power on, pour water into the sump and check for leaks. Reversed DC connections will spin the pump
impeller backwards and pump much less water.