Basically a drain gravity feeds the water to the filter rather than having a pump in the pond. The pump is then inside or near to the filter pumping water back into the pond, sort of reversing things a little. It is not essential for a standard pond but is essential really for a large koi pond and it can get a bit expensive, costing a few grand to do it properly. If all you want is a wildlife pond with goldfish then the normal pump-in-pond-to-filter sytem will be fine and a lot cheaper. I think 2010 did an article or something on it I will try to find it.
Ah, thanks for that Jaguar - it's a good job you're about today!!
I've been working my way through all of those, but I've also got some leaflets on how to set up a pond, and I've also looked around the internet.
We aren't going to have Koi - we are only doing this for Luke & Leia [our adopted goldies], but we're obviously going to add some some more as well!!
I think the size is going to be [approx] 24 feet by 4 feet and 4 feet deep I think it's going to be about 6 - 7,000 litres - I think [M's told me a couple of times but I don't keep numbers in my head very well ]
So it won't be suitable for Koi...but we should be able to have a few goldies in there.
Thanks for the links, I'll be going through them all....we've got to get this done this year, L & L are approx. 8 inches now, really should NOT be in a 180 litre tank!!
Dolhin Seabray 500 litres with four Fancy Goldies & 5 White Clo
You are going to need to fairly powerful pump and and filter for that size. If you are digging out to that depth you may as well go for the drain then. As the water pressure is going to be just enough. The dimensions you give makes a volume of around 10874 liters.
You can still use the pump-to-filter method but the filter will need to be at about the height of the waterfall if you are going to have one and you will need a pump and filter capable of shifting between 15-20000 litres per hour with a max head of twice or three times the height of the waterfall to get a good flow back down into the pond rather than a trickle.
You will need electric to the pond for a pump and filter, are you saying you cant get any electric to the pond?