@TraylerSailor
This gentleman owns a 240 with a lower ceiling. I received a private message and asked my dear friend, Peggie Hall, whose valuable information was handy based on a headroom of 1 foot 3 inches when the poster said it was 1 foot and 5 inches from the top of his head to the interior ceiling for her valuable response.
@Peggie Hall HeadMistress said:
A 2.5 gal portapotty holds 25-30 flushes, so 2-3 days is about right for 2 people continuously aboard. That size is also available as an MSD version, but it doesn't solve his need for more capacity.
However, it's pretty obvious that he hasn't actually checked the dimensions of the larger 5-6 gal MSD potties, he just "feels' they're too tall. I just checked 'em... the dimensions of the Dometic/SeaLand 970 series, the 5.5 gal MSD version is 15.5" tall, only 3" taller than the 2.5 gal model (see page 7
http://productimageserver.com/literature/ownersManual/37729OM.pdf) leaving him a full foot of headroom. The Thetford 550P MSD (see dimension in this Defender listing
Thetford 550P MSD on Defender ) is an inch taller than the SeaLand, leaving 11" above his head. How much more headroom does he need??? Either one holds 50-60 flushes, doubling his current capacity AND providing the convenience of being able to pumpout instead of having to carry out.
If that doesn't suit him a second tank is the only alternative I can think of, but it would have to be the same brand/model as the one he has and depending on the age of his boat, may or may not still be available.
Hope this helps...Happy New Year!
--Peggie
My thanks to Peggie for her time and research into this matter. Peggie, may you have a blessed and wonderful new Year