Sewerage build up in manhole

[Fromagep]

I have a modern circular manhole with 5 branches 2 of which are capped off.Toilet waste from the opposite 2 branches is building up in the exposed channels of the capped branches and on the benching.
At the moment I simply hose down the waste each week but wonder if there was some kind of fitting to divert waste down the pipe and to stop it splashing/accumulating in the manhole ?