Sale! Enquiry slimRain® Horizon Filter £150.00 £125.00 Exc. Vat The Horizon 100 filter is designed primarily for installation within a rainwater storage tank. Manufactured from high quality polyethylene and stainless steel. With only 52mm height difference between inlet and overflow, this filter can be fitted to most underground tanks. It can also be used externally to sit on top of an above ground tank if required.