Possible Clues:

• Boy loses head in drink, becoming something ugly
• Rainwater spout ending in a grotesque figure
• Grotesque mouthwash to drink only on vacation
• Good progress needed in shifting early architectural feature
• Ugly spout
• Royal egg (anag) — a drain on the church?
• Grotesque Gorgon's head, not a thing seen in Plymouth?
• Grey gaol designed by a frightening type that's found in the gutter perhaps
• Swill round, swallowing only in extremis? That’s grotesque
• Deform egg or lay monstrous one