Hi there. I have a '91 Macgregor
26s. Don't crank down on the valve too tight.. you'll compress the top of the ballast tank and could cause damage.
Keep a tub of vasoline with the boat
. Seriously. Coat the bottom of the top seal and the top of the bottom seal (in your pictures) with a fairly healthy coat. When you close the valve it will actually seal.
When lightly loaded (stock) you don't have to worry; when filling the ballast tank in the water
it won't overflow. When loaded to normal (camping/cruising/daysailing/two people on board/etc) levels, you do have to seal the valve after the water level in the tank gets within a finger's length of the air vent or it will overflow. I've had my '26 in a slip for a year and a half now without a haul out
, no leak from the valve with the vasoline on it. (Though I do have to keep adding some crushed chlorine tablet every few months through the vent hole to keep the hydrogen sulfide from building up due to anaerobic environment
. Hint -- if you crack the air vent and it stinks, don't breathe it in. let it air out before you go back into the boat)
Anyways great little boat, lotta fun, just went out for a pre-Rosa solo sail this past Saturday in Arizona in 12-20 kts, blast.