Humm... You must have a newer Cal. In any case, Skylark is correct. Any through-hull below the waterline should have a seacock to allow it to be closed when/if necessary. In re: cleaning, you may find an investment in a plumber's snake (or the rental of one) worth the investment. Depending upon your location, you may also find that critters have set up house-keeping in your drain-lines and need be removed to keep the lines clear.
"It is not so much for its beauty that the sea makes a claim upon men's hearts, as for that subtle something, that quality of air, that emanation from the waves, that so wonderfully renews a weary spirit."