Used to run my 30 opti up in an old dustbin, but a couple of times did not get the tell tale. Naturally shut off immediately. Advice from the Merc dealer was that running up in a bin is iffy, as you can get what is in effect a feed back loop with the intake picking up gas from exhaust, prop thrashing around etc. Natually, particularly applies if the 'tank' is on the smaller size.
When I got the XS the advice was flush it through on muffs, but only on tick over, and for no more than a minute. If that upsets the neighbours, then I would suggest let them get on with it