You have a soakaway and you still need to get it emptied?
Our one in France has yet to be emptied! It exits to a pipe which goes 250 feet and then joins the "mains drain" which isn't really hence we were obliged to put in a septic tank.
We had it inspected last summer and it was deemed OK. It went into the ground in 2008.
Admittedly we don't use it all year round, But there are two of us and, Covid and Brexit permitting, we have been there six months every year since 2015.
Friends in the village, who are there far more than us and had their house built by the same people as us, at least a year before ours, have also never had theirs emptied. And theirs exits like yours under the land in a typical crowsfoot.
Me no unnerstan!