If you have dual fuel tanks or water tanks, just adjust their level to counter that list. Our shower will drain when perfectly level but if there is even the slightest lest to Starboard we have a similar issue. Foggy gave good solutions that work well, but I find it is easy to just keep the fuel/water adjusted so that when we will be using the shower I have just a tiny list to Port.
If I have a tiny list to starboard due to fuel/water levels, I just transfer 30 gallons of fuel from Starboard to Port and all is well.