Pride and groom, the shedder shampoo. Works well for him.
i also have this vacuum attachment whic is great and keeps all the fur contained in the vacuum bag. He’s 10 and I have quite an accumulation of vacuum bags of gsd fur.
fyi I this attachment fits an old cheap vacuum, I don’t use it on a dyson vacuum.
https://www.amazon.com/Dyson-Groom-Tool-Vacuum-Assisted-Groomer/dp/B004CLPJRC?source=ps-sl-shoppingads-lpcontext&ref_=fplfs&psc=1&smid=A1O8AE65PG31SQ