This site has changed much over the years and is now a shadow. There are two places where you can view the settling beds

One from a bridge over the M4 at Cippenham and the other from the north bank of the Jubilee River Reserve

For both viewing points you'll need a scope. Migration is the best time to visit when you could get Curlew sand, godwits, wood sand, little stint (see even more link),  Pectoral sandpiper, Green-winged teal ...

Google maps link

Slough Sewage Farm