Fosse Septic

Hello everyone. I have had my builder convert part of my utility room into a proper toilet and washroom. Looks great. Hes done a good job.

I have a stone house, built early 19th cent.Currently renovating it.
However , after one of my artisans used the toilet it overflowed and on informing my builder, he said he had checked it. Advised to get septic tank emptied. This was done today. However, on flushing pipe next to toilet, on outside wall ( new loo) water blasted and shot out of middle of garden. Watery faeces. Hence, no problem with upstairs toilet just this new one.
Have someone coming next week to investigate this ? A broken pipe.
Questions: Anyone else had this problem?
? If digging area up will it be expensive.? Fosse man marked spot with a wooden steak.
Thank God for upstairs loo which travels to tank from another area.
Thanks in anticipation.

Sorry typo stake

I would have thought you would want the builder back as clearly he has not done something properly ? I also assume he has been paid and provided a Devi / facture for the work and has insurance ?

As has already been suggested… correct procedure is to get the builder who did the work… to come back and rectify.
He should have Insurance which covers him and his workmanship and the products/whatever he used…

It should be rectified Free of Charge for you…

Don’t let anyone else touch it, but him … is my best advice… but in the end, the decision is down to you…