Can someone please advise?

I have a Klargester septic system tank with an out flow piped into a collector tank. Due to the height of the local water table, a pump is used to take the water from the collector tank to a distribution box and on to the absorption field. The whole set up is now 4 years old but has had two problems from day 1. 

Firstly there is a strong sewage smell when the pump is running. This smell seems to be coming from the cover over the distribution box at the start of the absorption field. Is this normal (my neighbor has the same system and the same problem) and is there anything that can be done to reduce / stop it?

The second problem is the durability of the pump / float switch. I’ve had 3 pumps and 4 float switches in 4 years. The first I know about the failure is when the drains start to gurgle or the electric RCD trips out. The pump is a Clarke heavy-duty sewage cutter pump rated at 240 l/min and 400W with a maximum head of 8m. Can anyone recommend a better / more reliable set up and from where can I buy such a thing (preferably in the UK).

Thanks in advance.