I have had difficulty in identifying the type and manufacturer of my gully trap. Recently I noticed the rubber bung which covered the rodding eye hole has disappeared (probably flushed into the drain and taken a long dark journey!!
The trap is made completely of plastic, is square at the top where the grill fits into four locating pegs at the corners. Further down it changes to a round section which has a solid shroud covering the outlet which protrudes above the water level but leaves a gap at the bottom for water to flow; it is in the top of this shroud where the hole where the rubber bung should be. The hole is about two to two and a half inches in diameter.
The trap is cemented into the path and would take substantial effort to replace, so if I can get a replacement bung it would make life easier - even if I need to buy a complete trap to achieve this.
First stop - Measure the hole exactly.
Second stop - your local plumber/builder merchant
Desperation if all else fails - make a wooden bung very slightly smaller and paint it then wrap with insulation tape to get it an exact fit.
You can get bungs for motorcycle exhausts to stop water entering when washing. You may be able to get one large enough and cut it at the correct point on the taper.Using one in the washing line holder at the moment.
Self-amalgamating-tape (it's black and sticky & about an inch wide...I used it as a BT engineer for temporary joint closures) wrapped around the DIY bung as hinted by wiz-king might help to provide a good seal for a few months.
I have been searching against suggested manufacturers (and suppliers) with no success at finding a drawing/picture that remotely resembles the item - I think my next option is to visit all the builders merchants in the area.
As for making a replacement, I have considered various materials/methods but have rejected each on the grounds of complexity, longevity and/or effect to the system if lost again.
I have also looked at using a suitably sized rubber ball which appears to be viable as, unless forced into the downstream side of the trap, it cannot be lost due to its size.