The Natural Philosopher wrote:

yes. The only downside is pongs. If these are floating up from gulleys
or plugholes, then consider trapping those individually. Or source a
rubber plug from somewhere that fits. Or modify what you have to take
a standard rodding point.

Forgot about those.
To the OP, you can buy a rubber bung with a butterfly screw which tightens
and seals the hole, they are made specifically for drains and you can get
one from any builders merchant, or maybe even b&q.

Look for drain test plug on google, a 200mm (4 in) one will set you back
about 8 - 10 quid

--
Phil L
RSRL Tipster Of The Year 2008