Dude, that is cool as ****! That's a blister, back, ball breaking endeavor. The best thing is, after all that hard work, the fish that live there will be loved more because YOU put the work into their home!
Thanks putting in a retro fit bottom drain so pipe work is not in the concreate, then gravity fed filter chamber in my shed. Will use my big box filter off my old pond for now, might have a second hand vortex filter off my local petshop owner if the price is right. Lots more blockwork to do first and need to finish top end.