I have just bought a house where the previous owner has left a half finished
downstairs shower room. I wish to finish the job.
However, the soil pipe run does not have enough drop on it. I was thinking
of raising the floor (on 6x2's) to allow for enough drop on the soil waste
pipe.

I also need to connect the basin and shower waste to the same soil waste
pipe and I see you can buy strap on bosses for this.

Does the basin and shower boss have to enter at the top of of the 110mm soil
pipe (to avoid any back flow from WC) or can they connect on the side?

If they have to enter on top I may have raise the shower even higher to get
enough drop on the shower waste.

I know a macerator will solve these problems but i'm trying to avoid that
option if at all possible.

Any advice would be much appreciated.

MTIA