Square plunger for square gulley?

Our kitchen sink drains into a gulley, and over Christmas this blocked. We had the drains jetted and the drain man suggested we buy a drain rod-based plunger and use it once a month to try and keep the drains clear.

Lifting the gulley grid, I can see that the vertical pipe is square (5" x 5") but I can't find square plungers anywhere! Any ideas? I prefer the idea of a drain rod-based plunger if possible so I can do it from a standing position.

I wondered about buying a round plunger disc and cutting it down however I would need 7.1" or more to give a 5" square and the largest I can find is 6".

Any help appreciated.

A round plunger always achieves the desired effect on a gulley, even if the splashback is not so desirable.... To be honest plunging it is only going to send any detritus in the bottom of the pot into the sewer, where it could cause a problem elsewhere. Best advice IMO is to avoid putting any excess fat/grease, food waste, etc down the sink, and if you really want to clean it out buy a cheap wet vac.

Such as http://www.wickes.co.uk/invt/215735 It's noisy but does what it says on the box. This will allow you to remove any crud and not wash it further into the system!

Sometimes tricky with solid fat blocking the outflow at the bottom of gully. Sometimes the best way is the long rubber glove and something like a small flexi scraper or bendable plastic pipe to break up the blockage in the outflow. Not pleasant though,

The weird thing is, the blockage wasn't fat/grease as I expected, but solidified detergent. The drainage bloke could see I was sceptical so retrieved a big chunk to show me - it looked like the stuff they make dishwasher tablets out of and was powdery to the touch! It wasn't caustic soda "cement" either, I don't put soda in my drains as I have heard horror stories about cement forming.

I hadn't thought of using a wet-vac to drain the gulley, we were bailing it out on hands and knees. Will try that and the bendy plastic pipe if/when it blocks again (presumably something like 15mm plastic pipe?)

Thanks!