Easy enough if you know what you're doing, the hardest part would be digging the hole. Assuming existing drain is 110mm plastic, just expose enough pipe to accommodate the chamber and get a coupling in. Cut pipe and chamfer ends, fit chamber onto one cut end, with a stub of pipe in the other end to meet other end of existing pipe where you've cut it, then use a Slip Collar to join that together. Clayware drains similar idea, just use Flexseal couplings to join up instead.