Hi valued customer,
Thank you for your review of the Delta Faucet model 4159-BL-DST. Please accept our sincere apology for the inconvenience you are experiencing. We are happy to help.
To first troubleshoot a leak under the handle, securely tighten the bonnet with a wrench. Check that the hose clip is installed over the shoulders of the hose connection as shown in the manual.
https://images.thdstatic.com/catalog/pdfImages/01/01afb345-cfa0-453e-acd3-a620c81af760.pdf
As the manufacturer, we are committed to supplying you with a quality product that delivers the expected performance. Please contact us directly for assistance or if you have any questions!
Best Regards,
Bryan
Digital Communications Specialist
(800) 345-3358
customerservice@deltafaucet.com