I just bought a 2002 Sea Ray 240 Sundeck and had a similar experience. The pump or the fixture could be clogged and needs to be cleared. Take the strainers off each fresh water connection or hose and run at each you will notice the pressure increases and you will see some of the gunk caught by the strainers. You also check the water filter screen. The water pump is on the port side of the engine compartment and the filter is on the right side of the pump. Turn off the power to the pump and clean it. It should clear the lines. Fill the water tank ( standard 310 has a 28 gallon tank) add fresh water and add bleach a 1/2 cup should be good to sanitize. Run the each tap so the bleach reaches each fixture. My Sundeck has 3 was washdown houses and when I ran thru this they work like new.
