After a fresh installation of LXDE on Ubuntu 18.04, the tap gesture did not work for the touchpad of my Lenovo Y510P.

Installing Synaptics as  helped to solve the problem:

Previously, xserver-xorg-input-libinput  was installed, and I did not manage to configure the tap gesture using this driver, properly.

I found this solution on askubuntu.com.

The touchpad of the Lenovo Y510p laptop has no extra mouse buttons, but only soft-buttons below the surface. With the default settings, Kubuntu 14.04 recognizes a click on a soft-button additionally as move of the cursor, which led to imprecise behavior of the curosr.

KDE uses synaptiks to configure the touchpad. The option AreaBottomEdge can be used to set the y position of the bottom of the touchpad area (see man synpatiks for details).

It is sensible not to change the original synaptiks configuration, but to work with a copy, because the configuration file may be overridden by other tools:

In the new file, add the AreaBottomEdge option to the input device with identifier “Default clickpad buttons”. For me, it worked well with an area of 20% for the soft buttons.

The new settings will be read when the X server gets restarted (e.g. by pressing Ctrl-Alt-Backspace, if enabled).

If everything works fine, the new option is reflected in /var/log/Xorg.0.log after the next start of X: