On 19 Jan, 20:27, "The Medway Handyman"
wrote:
....
One old boy came up with a 'solution'. *Put several elbows in the waste
pipe, to take it down to floor level, under the unit, back up the other side
& reconnect to the waste - effectively forming a huge 'U' in the waste pipe.
....
Surely it wouldn't work?

It would work up until the point when it didn't :-)

Others have already discussed the issues, I'd add that :-

a) Sods law applies and any failure would be at the worst possible
time
b) From your description, access to resolve the problem could well be
difficult

Ignore the suggestions that you do it but give a disclaimer - that's a
recipe for later arguments and loss of goodwill. If you implement it,
you will be asked to fix it when it breaks.

My recommendation is that you suggest one or more workable solutions -
others have suggested a few - and if the church won't accept one of
them, politely decline the job.