Palm Desert-based U.S. Filter Corp. said it boosted its offer to buy the 94.8% of Memtec Ltd. shares it doesn't own to $36 a share, an offer accepted by Memtec directors. The bid, raised from $34.50 a share, values the company at about $380 million. It's the second time U.S. Filter has raised its bid for Memtec, based in Sydney, Australia. U.S. Filter wants Memtec's Memcor municipal water filtration system, which cleans water cheaply. In New York Stock Exchange trading, Memtec's American depositary receipts rose 19 cents to close at $35.75, and U.S. Filter shares rose 81 cents to $31.88.