Can I pipe basin waste into toilet flush pipe?

[RrogerD]

Wow thats so far out the question never even registered, perhaps he can just loop the waste pipe over the seat and just be careful when he sits down

Why is it "out of the question"? I am struggling to see the issue.
Sure I could end up with the wash-basin water sitting in the loo until it is next used but, we're only talking water mainly, not soap. It is an outside loo. It may be used to wash hands after gardening I guess.
There isn't the option to plumb it into the toilet waste as the ceramic part of the loo goes straight down into the hole in the ground.
I suppose syphoning could be a concern but as fixitflav says above, that shouldn't be a problem as it's all open to the elements anyway.

Sadly, I'm heading towards removing the sink altogether rather than have the waste simply 'dumping'out on to the lawn.

 

[dilalio]

Just try it.
Nothing to lose apart from maybe sacrificing the flush pipe.
Better than on the lawn.
It's an outside loo, can't see a major issue.