John,
This can be a problem on the Shannon.I'm sorry to hear that Dromineer is not up to scratch. It is a County Council facility and a note to them might remind them to give it a once over.
Your best bet elsewhere is to use the toilets at a quiet time or if you can identify the manhole on the drain empty direct into that. Essential kit for using the Elsan includes a roll of kitchen towel to mop up inevitable drips etc. Also a short hose with a union clip type connection is useful for getting tap water for the rinse out.
I don't know of any disposal points on the canal. Even toilets are in short supply so you may have to go to a petrol station.
The Shannon-Erne has the best Elsan facilities.
Paddy